Note: This method is only intended to use for batch processing of large
amounts of records that wouldn't fit in memory all at once. If you just
need to loop over less than 1000 records, it's probably better just to
use the regular find methods.

Yields each batch of records that was found by the find options as
an array. The size of each batch is set by the :batch_size option;
the default is 1000.

You can control the starting point for the batch processing by supplying
the :start option. This is especially useful if you want multiple
workers dealing with the same processing queue. You can make worker 1
handle all the records between id 0 and 10,000 and worker 2 handle from
10,000 and beyond (by setting the :start option on that worker).

It's not possible to set the order. That is automatically set to
ascending on the primary key (“id ASC”) to make the batch ordering work.
This also mean that this method only works with integer-based primary keys.
You can't set the limit either, that's used to control the the
batch sizes.

Example:

Person.where("age > 21").find_in_batchesdo|group|sleep(50)# Make sure it doesn't get too crowded in there!
group.each{|person|person.party_all_night!}end

# File 'activerecord/lib/active_record/relation/batches.rb', line 50deffind_in_batches(options={})relation=selfiforders.present?||taken.present?ActiveRecord::Base.logger.warn("Scoped order and limit are ignored, it's forced to be batch order and batch size")endif(finder_options=options.except(:start,:batch_size)).present?raise"You can't specify an order, it's forced to be #{batch_order}"ifoptions[:order].present?raise"You can't specify a limit, it's forced to be the batch_size"ifoptions[:limit].present?relation=apply_finder_options(finder_options)endstart=options.delete(:start).to_ibatch_size=options.delete(:batch_size)||1000relation=relation.except(:order).order(batch_order).limit(batch_size)records=relation.where(primary_key.gteq(start)).allwhilerecords.any?yieldrecordsbreakifrecords.size<batch_sizeifprimary_key_offset=records.last.idrecords=relation.where(primary_key.gt(primary_key_offset)).to_aelseraise"Primary key not included in the custom select clause"endendend